Pressure switches are used in myriad systems and environments to sense a media pressure and, when the sensed media pressure attains a predetermined media pressure value, to change a switch state or states. The switch state change can then be used to cause particular desired action such as, for example, the energization or deenergization of an alert, a pump, or a valve actuator.
Most pressure switches typically include a pressure sensitive mechanism and a resiliently biased switch. One particular type of pressure switch is implemented using a spring-loaded piston as the pressure sensitive mechanism. The spring supplies a pre-load to the piston that urges the piston toward a first position. With this pressure switch, when a media pressure applied to the piston supplies a force that exceeds the preload force of the spring, the piston begins moving away from the first position. If the media pressure continues to increase, the piston will contact the resilient switch, and begin urging the resilient switch from an initial state (e.g., either open or closed) toward a second switch state (e.g., either closed or open). If the media pressure continues to increase and attains or exceeds a predetermined pressure magnitude, the piston will move the resilient switch to a second position.
Thereafter, if the media pressure decreases, the piston will begin moving, with the assistance of the spring, from the second position toward the first position. If the media pressure continues to decrease, at one or more predetermined pressure magnitudes the switch will move from its second switch state to its initial switch state and the piston will move back to its first position.
Preferably, pressure switches, such as the one described above, are configured to exhibit some level of pressure switching hysteresis. That is, a difference in the pressure-increasing and pressure-decreasing set points. Historically, pressure switches have used snap-action Belleville washer springs to implement this hysteresis. However, this typically requires the various mechanical components that comprise the pressure switch to be held to relatively tight tolerances, which can increase overall manufacturing costs. Moreover, the adjustability of the hysteresis of present pressure switches is either relatively small or non-existent.
Hence, there is a need for a pressure switch that is configured to exhibit pressure switching hysteresis and that does not rely on relatively tight tolerances for the components that comprise the pressure switch and/or allows for greater adjustability of the pressure switching hysteresis. The present invention addresses one or more of these needs.